与JPA独特约束的交易丢失？

Question

我有一个独特约束的领域：

@Column(unique=true)
private String uriTitle;

当我尝试保存具有相同值的两个实体时，我会得到一个例外 - 但另一个例外，而不是我所移动的另一个例外：

java.lang.IllegalStateException: <|Exception Description: No transaction is currently active
        at org.eclipse.persistence.internal.jpa.transaction.EntityTransactionImpl.rollback(EntityTransactionImpl.java:122)
        at com.example.persistence.TransactionFilter.doFilter(TransactionFilter.java:35)

可疑的过滤方法看起来像这样：

public void doFilter(ServletRequest request, ServletResponse response,
          FilterChain chain)
          throws IOException, ServletException {
    EntityManager entityManager = ThreadLocalEntityManager.get();
    EntityTransaction transaction = entityManager.getTransaction();
    transaction.begin();
    try {
      chain.doFilter(request, response);
      transaction.commit();
    }
    catch (Throwable t) {
      transaction.rollback();  // line 35, mentioned in the exception
      throw new RuntimeException(t);
    }
    finally {
      entityManager.close();
      ThreadLocalEntityManager.reset();
    }
}

...以及像这样的threadLecalentityManager：

public class ThreadLocalEntityManager {

    private static EntityManagerFactory entityManagerFactory = null;
    private static final ThreadLocal<EntityManager> entityManager =
        new ThreadLocal<EntityManager>() {
            @Override 
            protected EntityManager initialValue() {
                return entityManagerFactory.createEntityManager();
            }
        };

    private ThreadLocalEntityManager() {}

    public static synchronized void init(String persistenceUnit) {
        requireNotNull(persistenceUnit);
        requireState(entityManagerFactory == null, "'init' can be called only "
                        + "once.");
        entityManagerFactory =
                        Persistence.createEntityManagerFactory(persistenceUnit);
    }

    public static EntityManager get() {
        requireState(entityManagerFactory != null, "Call 'init' before calling "
                        + "'get'");
        return entityManager.get();
    }

    public static void reset() {
        entityManager.remove();
    }

}

我把电话包裹了 save 和 try ...catch 处理独特的约束违规行为，但这无效：

try {
    ThreadLocalEntityManager.get().persist(article); // article is constrained
}
catch(Throwable t) {
    t.printStackTrace();
}

知道为什么没有交易吗？处理独特的约束违规的正确方法是什么？

Answer 1

由于违反数据库的约束，您的交易自动回滚，因此没有手动回滚的交易。要处理这种情况，您可以写

catch (Throwable t) {
  if (transaction.isActive()) 
    transaction.rollback();  // line 35, mentioned in the exception 
  throw new RuntimeException(t); 
}

Answer 2

您的应用程序中的交易和GUI之间没有任何分离。一般而言，您将在交易处理方面遇到问题。